<?
require_once('Core.php');

try{
	// Get a semi-random ID to identify this request within the log.
	$requestId = substr(sha1(time() . rand()), 0, 8);

	Logger::WriteGithubWebhookLogEntry($requestId, 'Received GitHub webhook.');

	if($_SERVER['REQUEST_METHOD'] != 'POST'){
		throw new WebhookException('Expected HTTP POST.');
	}

	$post = file_get_contents('php://input');

	// Validate the GitHub secret.
	$splitHash = explode('=', $_SERVER['HTTP_X_HUB_SIGNATURE']);
	$hashAlgorithm = $splitHash[0];
	$hash = $splitHash[1];

	if(!hash_equals($hash, hash_hmac($hashAlgorithm, $post, preg_replace("/[\r\n]/ius", '', file_get_contents(GITHUB_SECRET_FILE_PATH))))){
		throw new WebhookException('Invalid GitHub webhook secret.', $post);
	}

	// Sanity check before we continue.
	if(!array_key_exists('HTTP_X_GITHUB_EVENT', $_SERVER)){
		throw new WebhookException('Couldn\'t understand HTTP request.', $post);
	}

	$data = json_decode($post, true);

	// Decide what event we just received.
	switch($_SERVER['HTTP_X_GITHUB_EVENT']){
		case 'ping':
			// Silence on success.
			Logger::WriteGithubWebhookLogEntry($requestId, 'Event type: ping.');
			throw new NoopException();
			break;
		case 'push':
			Logger::WriteGithubWebhookLogEntry($requestId, 'Event type: push.');

			// Get the ebook ID. Our repo names are simply the Gutenberg ebook ID number.
			// PHP doesn't throw exceptions on invalid array indexes, so check that first.
			if(!array_key_exists('repository', $data) || !array_key_exists('name', $data['repository'])){
				throw new WebhookException('Couldn\'t understand HTTP POST data.', $post);
			}

			$repoName = trim($data['repository']['name'], '/');

			if(in_array($repoName, GITHUB_IGNORED_REPOS)){
				Logger::WriteGithubWebhookLogEntry($requestId, 'Repo is in ignore list, no action taken.');
				throw new NoopException();
			}

			// Get the filesystem path for the ebook ID.
			$dir = REPOS_PATH . '/' . $repoName . '.git/';

			// Confirm we're looking at a Git repo in our filesystem
			if(!file_exists($dir . "HEAD")){
				throw new WebhookException('Couldn\'t find repo "' . $repoName . '" in filesystem at "' . $dir . '".', $post);
			}

			Logger::WriteGithubWebhookLogEntry($requestId, 'Processing ebook "' . $repoName . '" located at "' . $dir . '".');

			// Check the local repo's last commit. If it matches this push, then don't do anything; we're already up to date.
			$lastCommitSha1 = trim(shell_exec('git -C ' . escapeshellarg($dir) . ' rev-parse HEAD 2>&1; echo $?'));

			if($lastCommitSha1 === null){
				Logger::WriteGithubWebhookLogEntry($requestId, 'Error getting last local commit. Output: ' . $lastCommitSha1);
				throw new WebhookException('Couldn\'t process ebook.', $post);
			}
			else{
				if($data['after'] == $lastCommitSha1){
					// This commit is already in our local repo, so silent success
					Logger::WriteGithubWebhookLogEntry($requestId, 'Local repo already in sync, no action taken.');
					throw new NoopException();
				}
			}

			// Now that we have the ebook filesystem path, pull the latest commit from GitHub.
			exec('/standardebooks.org/scripts/pull-from-github ' . escapeshellarg($dir), $output, $returnCode);
			if($returnCode != 0){
				Logger::WriteGithubWebhookLogEntry($requestId, 'Error pulling from GitHub. Output: ' . implode("\n", $output));
				throw new WebhookException('Couldn\'t process ebook.', $post);
			}
			else{
				Logger::WriteGithubWebhookLogEntry($requestId, 'git pull from GitHub complete.');
			}
			break;
		default:
			throw new WebhookException('Unrecognized GitHub webhook event.', $post);
			break;
	}

	// "Success, no content"
	http_response_code(204);
}
catch(WebhookException $ex){
	// Uh oh, something went wrong!
	// Log detailed error and debugging information locally.
	Logger::WriteGithubWebhookLogEntry($requestId, 'Webhook failed! Error: ' . $ex->getMessage());
	Logger::WriteGithubWebhookLogEntry($requestId, 'Webhook POST data: ' . $ex->PostData);

	// Print less details to the client.
	print($ex->getMessage());

	// "Client error"
	http_response_code(400);
}
catch(NoopException $ex){
	// We arrive here because a special case required us to take no action for the request, but execution also had to be interrupted.
	// For example, we received a request for a known repo for which we must ignore requests.

	// "Success, no content"
	http_response_code(204);
}
?>